copyright © 2015 cengage learning® 1 chapter 6 safe dosage calculations

Copyright © 2015 Cengage Learning® 1Copyright © 2015 Cengage Learning®

Chapter 6Safe Dosage Calculations

Copyright © 2015 Cengage Learning® 2

• Calculation, preparation, and administration of safe dosages– Key principle: do no harm

• Medication must be administered exactly as prescribed and in the appropriate dose

• Unit-dose form– Each individual dose of medicine is

prepackaged in a separate packet, vial, or prefilled syringe

Introduction


Calculation Guidelines• Know basic arithmetic• Take meticulous care with all calculations• Calculate ordered dosage from what is on

hand – Check whether measures are in the same

system and convert if necessary – Write the problem in an equation and complete

the necessary calculations– Check accuracy and have someone verify


Method 1: Basic Calculation• Formula:

, i.e.,

– Example: The physician orders 162mg of

aspirin q4h PRN for fever over 101° • On hand are aspirin 81 mg aspirin tablets


Method 1: Basic Calculation (cont’d.)

• What are the cautions for this method?– Label all parts of the formula– Use the same label for desired and on-hand

doses– Use the same label for the quantity and the

answer (the amount to be given)– Reduce fractions to lowest terms before

dividing


Method 1: Basic Calculation (cont’d.)

– Multiply by the quantity after dividing– Take extra care with decimals– Convert fractions to decimals– Round off decimals to one decimal place after

computation is complete– Verify the accuracy of calculations with an

instructor– Question the answer if not within normal limits


Method 2: Ratio and Proportion• A ratio describes a relationship between

two numbers– Example: 1 g : 15 gr

• A proportion consists of two ratios that are equal– Example: 1 g : 15 gr = 2 g : 30 gr


Method 2: Ratio and Proportion (cont’d.)

• Procedure– Always label each term in the equation– Terms of each ratio must be in the same

sequence– Set up the formula with known terms on the

left and desired and unknown terms on the rightknown unit : known = desired unit : unknown

of measure equivalent of measure equivalent


Method 2: Ratio and Proportion (cont’d.)• Formula:

• Example:– Preoperative order reads Demerol 60 mg IM

on call• Narcotics drawer contains vials labeled meperidine

(Demerol) 100 mg/2 mL

dose : known = dose : unknown on hand quantity desired quantity



• What are the cautions for this method?– Label all parts of the equation– Ratio on the left contains the known quantity,

and ratio on the right contains desired and unknown quantities

– Terms of second ratio must be in the same sequence as those in first ratio

– Multiply extremes first and then the means– Take extra care with decimals



– Convert fractions to decimals– Round off decimals to one decimal place– Label the answer– Verify the accuracy of calculations with an

instructor– Question any unusual dosage not within

normal limits


Pediatric Dosage• Children are not miniature adults

– Appropriate dosage must take into consideration age, weight, sex, and metabolic, pathological, or psychological conditions• Always refer to recommended dosages as listed in

drug inserts, Physicians’ Desk Reference (PDR), or AHFS Drug Information (AHFS DI)


Pediatric Dosage (cont’d.)• Example:

– Recommended dose of meperidine (Demerol) is 6 mg/kg/24 h for pain, in divided doses every four to six hours, as necessary

– Demerol is available in ampules or cartridges labeled 50 mg/mL

– How much Demerol would be appropriate for a 33-pound child as a single dose every six hours?


Pediatric Dosage (cont’d.)• Convert pounds to kilograms (divide

number of pounds by 2.2):


Pediatric Dosage (cont’d.)• Calculate the number of milliliters needed

in 24 hours

dose : known = dose : unknown on hand quantity desired quantity


Pediatric Dosage (cont’d.)• Calculate the number of milliliters needed

in six hours


Pediatric Dosage (cont’d.)• Appropriateness of this dose can be

checked by applying Clark’s Rule


Pediatric Dosage (cont’d.)• Demerol is available in ampules labeled

100 mg/2 mL


Geriatric Dosage• Give special consideration to preparation

and administration of safe dosage to older adults– The dose frequently needs to be reduced

• Several factors lead to possible dangerous cumulative effects – Slower metabolism, poor circulation, or

impairment of liver, kidneys, lungs, or central nervous system


Geriatric Dosage (cont’d.)• No formula can guide you in safe geriatric

dosage– Assess carefully on an individual basis,

monitor constantly, and reduce dosage whenever possible


Prevention of Medication Errors• Medication errors

– Can occur for a number of reasons• How can these errors be prevented?

– Never leave the decimal point naked– Never place a decimal point and zero after a

whole number– Avoid using decimals whenever whole

numbers can be used as alternative


Prevention of Medication Errors (cont’d.)

– Have a second qualified person double-check any calculations for accuracy

– If you have difficulty interpreting the spelling of a drug name or the number used for the dosage, or the dosage seems inappropriate, always question the order

copyright © 2015 cengage learning® 1 chapter 6 safe dosage calculations

Documents

cengage learning

gr slide

basic calculation slide

equation ratio

normal limits slide

unknown terms

safe dosage calculations

accuracy of calculations